We report an infant with autoimmune neutropenia (AIN), idiopathic thrombocytopenia (ITP), and IgG2/IgA deficiency. The patient was referred to our hospital at 5 months of age because of epistaxis and generalized petechiae. Physical examination revealed moderate hepatosplenomegaly. A complete blood count revealed a platelet count of 2.0 x 10 (3) cells/microliters, and a white cell count of 3,600 cells/microliters, with severe neutropenia (less than 1% bands and segmented cells). Neutrophils and platelets adhering to megakaryocytes were decreased in the bone marrow. Tests for serum neutrophil-binding IgG (NB-IgG) and platelet-associated IgG (PA-IgG) were positive. A diagnosis of both AIN and ITP was made and therapy with intact-type gamma-globulin and prednisolone was initiated. Improvement occurred, but was temporary. A lack of serum IgA and IgG2 was noted during the clinical course. The patient has not been susceptible to bacterial infections but has had a severe clinical course with rubella and chickenpox.